Orgueil meteorite

A large carbonaceous chondrite that disintegrated
and fell in fragments near the French town of Orgueil on May 14, 1864. About
20 pieces, totaling about 12 kg in mass, were subsequently recovered from
an area of several square km, some head-sized but most smaller than a fist.
Specimens could be cut with a knife and, when sharpened, could be used like
a pencil. One specimen was immediately examined by the French scientist
S. Cloëz, who commented that its content "would seem to indicate the existence
of organized substances in celestial bodies." Subsequently, several eminent
chemists of the time, including Gabriel-Auguste Dubrée and Marcellin Berthelot,
analyzed samples and confirmed the existence of organic
materials in the rock. Coming at the same time as Pasteur's
famous announcement that he had experimentally disproven the theory of spontaneous
generation on Earth, these findings prompted a scientific debate about whether
such generation might be possible in space. Pasteur himself examined the
Orgueil meteorite, as recounted by Carl Sagan:

[He] caused a special drill to be constructed,
which, he hoped, would remove samples from the interior of the meteorite
without contaminating them with microorganisms from outside. Using sterile
techniques, Pasteur inoculated an organic medium to search for growth
of any indigenous microorganisms which the meteorite interior might contain.
The results were negative, and have relevance today: Pasteur extracted
his sample shortly after the fall of the meteorite, and was, of course,
a very careful experimentalist.

The possibility of biological remains in the Orgueil stone resurfaced, however,
a century later. At a meeting of the New York Academy of Sciences in March
1961, Bartholomew Nagy and Douglas J. Hennessy of the Department of Chemistry
at Fordham University's Graduate School of Arts and Sciences in the Bronx,
and Warren G. Meinschein, a petroleum chemist at the Esso Research and Engineering
Company in Linden, New Jersey, announced that they had found in a sample
of the meteorite "paraffinoid hydrocarbons," similar in type and distribution
to those occurring in animal products such as butter.1 From this,
they concluded that "biogenic processes occur and that living forms exist
in regions of the universe beyond the earth." More remarkably, Nagy and
George Claus, a microbiologist at New York University Medical Center, claimed
shortly after that samples from the Orgueil and Ivuna
meteorites contained "organized elements" including structures "resembling
fossil algae."2 A controversy ensued in which a minority of scientists,
including J. D. Bernal, supported the microfossil
theory, while most, including Philip Morrison
and Harold Urey were skeptical. Urey did, however,
concede that it was possible the Orgueil and Ivuna microstructures were
evidence for biogenic activity and that, if so, these meteorites may have
come from the Moon which "became contaminated temporarily with water and
life-forms from Earth early in its history."3 By 1975, Nagy himself
had come to regard the biological interpretation as a "remote possibility."

In 2001, the results of a new study of material from the Orgueil carried
out by a team from the Scripps Institution of Oceanography in California,
the Leiden Observatory in the Netherlands, and the NASA Ames Research Center,
were published.4 This study used sophisticated techniques and
instruments aimed at detecting trace levels of amino
acids. After obtaining a pristine piece of the interior of Orgueil,
the researchers found that it contained a relatively simple mixture of amino
acids, consisting primarily of glycine and
beta-alanine. They also analyzed the sample's
carbon isotope concentration and found that the amino acids were not derived
from Earthly contamination but instead were almost certainly synthesized
chemically in space. The research team then compared their results with
three other meteorites: Murchison and
Murray, which have been studied extensively,
and Ivuna, a meteorite that fell in Tanzania, Africa, in 1938, that had
not been analyzed for amino acids. The team broke the meteorites down into
two classes. The Murchison and Murray meteorites were placed in a category
containing a complex mix of amino acids made up of more than 70 different
types of amino acids. Orgueil and Ivuna, however, were categorized with
a much simpler composition made up primarily of just two amino acids. Based
on the unique amino acid composition within Orgueil, the researchers were
able to deduce information about the meteorite's past. Murchison and Murray
are widely believed to be pieces of an asteroid, as are virtually all meteorites
scientists have studied. However the paper suggests Orgueil and Ivuna show
evidence that they are likely derived from a comet.
The amino acid signatures within Orgueil and Ivuna suggest that these compounds
were likely synthesized from components such as hydrogen
cyanide, which have been recently observed in the comets Hale-Bopp
and Hyakutake. This suggests that the organic material in Orgueil and Ivuna
is the product of reactions that once took place in the nucleus of a comet,
which, if true, would make these meteorites the first to be identified as
having come from a cometary nucleus and add to the evidence that the amino
acids that helped generate life on Earth may have been delivered by meteorites
that were derived from the remnants of comets.

In 2004, the possibility of fossilized biological remains in Orgueil was
raised again by Richard Hoover of NASA's Marshall
Space Flight Center (MSFC). At the "Instruments, Methods, and Missions
for Astrobiology VIII" (Conference 5555) at SPIE's International Symposium
on Optical Science and Technology held in Denver, Colorado, August 2-3,
2004, Hoover showed images from a freshly fractured specimen of Orgueil
taken in July 2004 using the Environmental- and Field Emission Scanning
Electron Microscopy at MSFC in Huntsville, Alabama. These pictures appeared
to show forms in the meteorite that closely resemble mats of known terrestrial
fossilized cyanobacteria such as Phormidium
tenuissimum. Interestingly, on Earth, such cyanobacteria form their
mats only underwater on surfaces exposed to sunlight. However, the specimen
of Orgueil studied by Hoover has not been submerged since its arrival on
Earth (it would have dissolved), nor was its interior open and exposed to
sunlight on Earth before now. Furthermore, the putative fossils would not
represent isolated single cells, but whole ecologies. The implication is
that they must have grown on the meteorite's parent body before it fell.
However, as in the case of other claims regarding extraterrestrial fossils
aboard meteorites, this new piece of evidence is unlikely to be readily
accepted by the scientific establishment until it can be rigorously shown
that (a) the remains admit no non-biological interpretation, and (b) the
possibility of terrestrial contamination can be absolutely ruled out.